Arrange 1 rack in lower third and another rack in upper third of oven; preheat to 400°F. In a medium saucepan, bring 3 cups water to a boil. Stir in Kamut, reduce heat to medium-low, cover and simmer until tender and slightly chewy, 45 to 50 minutes. Drain and set aside to cool to room temperature.

Meanwhile, line 2 large rimmed baking sheets with foil and mist with cooking spray. In a medium bowl, toss squash with 1 tsp oil, 1/8 tsp salt and pinch pepper. Spread squash evenly across half of 1 sheet. In same bowl, toss Brussels sprouts with 1 tsp oil, 1/8 tsp salt and pinch pepper. Spread Brussels sprouts in an even layer on other half of sheet with squash. Transfer to lower rack in oven and roast for 20 to 25 minutes, turning halfway, until vegetables are tender and Brussels sprouts are lightly golden brown. Meanwhile, in same bowl, toss grapes with 1 tsp oil, 1/8 tsp salt and pinch pepper. Spread grapes evenly on remaining baking sheet. Roast grapes on upper rack for 15 minutes. Let cool to room temperature.